Generally, a six cylinder EB would have come from the factory with either 4.11 or 4.56 differential gearing. Great starting point for most of us!
Screaming is relative. The gearing and tire size dictate the rpm at any given road speed, no matter what engine is motivating it. But some sixes don't like revving up, that's for sure. Not sure what a good-running 170 likes to see, rpm-wise, but if it can spin up to 4500-5000 rpm like many non-diesel American engines could, then you can run just about any normal speed with it.
The V8's certainly get there sooner, and feel stronger throughout the rpm range generally. But as you found, at a relaxing pace and no big stressing out about speed, it can get the job done.
Not only actual engine speed, but muffler design, tire tread type and wear, and engine accessories (fans especially) all conspire together to make it sound like it's screaming down the road at higher rpm than it is sometimes.
What are 170's happy at anyway?
And what size tires are those? Look like 31's, but I suppose they could be 30's as well. Great looking Bronco for sure. Love the stance, and like many here I'm sure, the overall adventure-rig/rock hound look, like so many had back when this one was new.
Have lots of fun with it, and enjoy the waves, thumbs-up, and conversations at gas stations.
Paul